Spatiotemporal variability of fugitive gas migration emissions around a petroleum well

Fugitive Gas Migration in the Vadose Zone at an Experimental Field Site in the Montney Shale Gas Region

“…To accurately detect and monitor GM, it is important to understand site‐specific conditions at the time of assessment and to evaluate the potential for these processes to influence gas transport and fate. Current monitoring practices that rely on measurements in close proximity to an oil and gas wellhead during a one‐time monitoring event (Alberta Energy Regulator, 2021; BC Oil and Gas Commission, 2018; Fleming et al., 2021; Forde, Mayer, & Hunkeler, 2018) may over‐ or underestimate, or not detect GM and GHG emissions. As studies advance knowledge on the processes influencing fugitive GM in the vadose zone, efforts should be made to improve monitoring protocols.…”

“…This phenomena, "barometric pumping", has been observed in numerous global settings including landfills (Czepiel et al, 2003;Gebert & Groengroeft, 2006;Xu et al, 2014) and at contaminated sites (Choi et al, 2002). In some instances, fugitive CH 4 effluxes at oil and gas well pads have been moderately correlated with barometric-pressure changes, however, at these sites the responses were likely dampened due to a thin vadose zone (Fleming et al, 2021;Lyman et al, 2020). Forde et al (2019) demonstrated during an experimental natural-gas leak in a deep vadose zone, that the frequency and amplitude of barometric-pressure changes can directly control the magnitude and spatiotemporal distribution of CH 4 effluxes from the soil surface to the atmosphere (Forde et al, 2019).…”

“…This phenomena, “barometric pumping”, has been observed in numerous global settings including landfills (Czepiel et al., 2003; Gebert & Groengroeft, 2006; Xu et al., 2014) and at contaminated sites (Choi et al., 2002). In some instances, fugitive CH 4 effluxes at oil and gas well pads have been moderately correlated with barometric‐pressure changes, however, at these sites the responses were likely dampened due to a thin vadose zone (Fleming et al., 2021; Lyman et al., 2020). Forde et al.…”

“…Fugitive gas that reaches the ground surface and enters the atmosphere thereby contributes to greenhouse gas (GHG) emissions (Bachu, 2017; Lan et al., 2015; Lebel et al., 2020; Zavala‐Araiza et al., 2015). To identify the occurrence of GM, it is often a regulatory standard to collect shallow soil‐gas samples and/or measure efflux at the ground surface in close proximity to the oil and gas wellhead during a one‐time monitoring event (Alberta Energy Regulator, 2021; BC Oil and Gas Comission, 2018; Fleming et al., 2021; Forde, Mayer, & Hunkeler, 2018).…”

“…• Fugitive gas migrated to the ground surface despite a deep vadose zone with low-permeability silts and clays • A preferential pathway and intervals of decreased barometric pressure resulted in a hotspot with high episodic methane effluxes • Low-permeability sediments and intervals of increased barometric pressure favored lateral gas migration and progressive methane oxidation in barometric pressure (Fleming et al, 2021;Forde et al, 2019;Lyman et al, 2020), wind speed (Fleming et al, 2021;Ulrich et al, 2019), and differences between atmospheric and soil temperatures and associated temperature fluctuations (Fleming et al, 2021;Xu et al, 2014). As a result, measurements of emissions at the ground surface only provide a partial view of GM.…”